"I wanted that to be the last things they heard, not the gunfire in the hallway."

Editor's Note: Click here to read about another heroic first grade teacher, Victoria Soto, who died putting herself "between the children and the gunman" during the Connecticut school shooting Friday.

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First grade teacher Kaitlin Roig didn't think she and her students were going to survive.

When the gunfire started at Sandy Hook Elementary in Newtown, Conn. Friday morning, Roig rushed her 15 children into the class bathroom to hide. Her classroom had large windows, and she knew they needed to get somewhere safer.

"I just knew we had to get in there, I was just telling them it's going to be all OK, you're going to be all right," Roig told ABC News.

She pulled a bookshelf in front of the door to barricade them all inside. Hers was the first classroom in the hallway. She was thinking they were next.

"I told them we had to be absolutely quiet," Roig said. "Because I was so afraid that if he did come in, he would hear us and he would just start shooting the door. I said there are bad guys out there now, and now we have to wait for the good guys."

Roig said that if any of the students started crying, she would hold their face in her hands an tell them it was going to be OK. She said one of the students said they didn't want to die, they just wanted to have Christmas. Another said they just wanted to hug their mom.

"I said to them, I need you to know that I love you all very much and it's going to be OK, because I thought that was the last thing they were ever going to hear," Roig said. "I wanted that to be the last things they heard, not the gunfire in the hallway."

Roig said the gunfire didn't actually last very long, but even once it stopped she said they weren't leaving.

"I said we're not going anywhere, we're going to stay until someone good gets us out," she said.

But they didn't move, even when police started knocking. She worried it could be the gunman trying to lure them out.

"I said don't believe you, I said you need to put your badges under the door, so they put their badges under the door," she said. "I said if you're really a police officer you would have a way in here, you would have a key...so he had the keys and he found the right one."